Weed and grass trimmers have been developed which employ a rotatable hub with a short length of flexible nylon or other plastic line extending from the hub. When the hub is rotated (typically at speeds from 6,000 RPM to 12,000 RPM), the tip of the line extending from the hub provides the cutting or trimming action. Grass and weed trimmers using this principle of operation have become popular for their versatility of use and because the flexible trim line is safer to use than rigid rotating steel blades.
Various types of devices have been developed for using such trim lines. Typically, rotating line trimmers or rotating string trimmers employ a line which generally has a circular cross section. The line, in many trimmers, is wound on a storage reel in the hub of the device and is fed out of a hole in the hub in discrete amounts, as the end breaks off or wears off. Trimmers of this type sometimes are referred to as "bump and feed" trimmers, since, when the line breaks off, the bottom of the storage reel is bumped on the ground to cause a spring release of the line within the trimmer, which then plays out a short length of line through a hole in the hub by means of centrifugal force when the trimmer is operating. Typically, the smaller (with 21/2" diameter to 31/2" diameter head) bump and feed string trimmers use the relatively small diameter line, normally in the range of 0.065" to 0.080" diameter, since the smaller diameter flexible line functions better for the centrifugal feeding of such a smaller diameter bump and feed head.
The reason that small diameter line is used in bump and feed string trimmers is that heavier diameter line (for example, 0.115" to 0.160" diameter) typically is too stiff for winding and for the centrifugal feeding used in bump and feed heads. Commercial bump and feed heads use a larger diameter head than was designed for home use, and operate with somewhat larger diameter flexible line, generally from 0.95" to 0.105" diameter and normally have a larger capacity for such line. Thus, less frequent reloading of the line is required.
A problem exists with bump and feed trimmers, however, in that frequently the line which is wound on the storage reel in the hub tends to become stuck, either due to partial fusion of the line within the hub, caused by high frequency vibration, or by successive turns of the line wound on the hub becoming somewhat entangled. As a result, feeding of the line from the hub, when desired, does not take place. When this occurs, it is necessary to remove the hub from the string trimmer device and manually extract the desired length of line prior to reattaching the hub to the device. This is a very time consuming and frustrating experience for many users of flexible line string trimmers.
For commercial use employing relatively large diameter lines, for example 0.115" to 0.160" diameter, fixed-line trimmer heads usually are employed. The large diameter monofilament nylon lines are particularly useful where weed and grass growth is dense. The large diameter lines also provide longer length of service before the line needs to be replaced. Due to the hole design and pattern, smaller standard sized lines (under about 0.095" diameter) have a tendency to slip out of commercial fixed heads during operation.
One type of fixed line trimmer head for commercial use is the Echo.RTM. heavy duty fixed line trimmer head, stock No. 999442-0020. This trimmer head is designed to replace a saw blade trimmer/brush cutter or other types of flexible line trimmer heads. The Echo.RTM. trimmer head is open on its underside and provides serpentine paths for the insertion of two fixed lengths of 0.130" diameter monofilament nylon line. The line is inserted between closely spaced, offset guide surfaces to hold it in place during operation. When a new length of line needs to be inserted, the old line must be removed, and the new line guided in place around the guide surfaces. Because the guide surfaces are close together and 0.130" diameter line is relatively stiff, it is difficult to install and remove sections of nylon line from the Echo.RTM. trimmer head. This difficulty results in excessive time being consumed for the removal and replacement of line segments.
Another fixed-line trimmer head is known as the Grass Terminator.RTM. replacement head, designed for replacing the "bump and feed" spool cartridges of a variety of line trimmer machines designed for home use. The Grass Terminator.RTM. fixed head also employs guide paths for feeding two segments of line into and out of the head. The guide paths used with this head, in some cases, tend to allow the line to be pulled out of the head when it strikes an obstruction such as a chain link fence or the like, particularly when the small diameter trim lines for which it is designed are used.
Accordingly, it is an object of this invention to provide an improved fixed-line trimmer head for string trimmer machines which overcomes the disadvantages of the prior art, which may be used as an alternative to bump and feed cartridges, which is easy to load and replace, and which securely holds fixed segments of line of different sizes in place during use.